mirror of
https://sourceware.org/git/binutils-gdb.git
synced 2024-11-26 11:33:45 +08:00
264 lines
7.6 KiB
Plaintext
Executable File
264 lines
7.6 KiB
Plaintext
Executable File
_dnl__ -*- Texinfo -*-
|
|
_dnl__ Copyright (c) 1991 Free Software Foundation, Inc.
|
|
_dnl__ This file is part of the source for the GDB manual.
|
|
@c M4 FRAGMENT: $Id$
|
|
@node Sample Session, Invocation, New Features, Top
|
|
@chapter A Sample _GDBN__ Session
|
|
|
|
You can use this manual at your leisure to read all about _GDBN__.
|
|
However, a handful of commands are enough to get started using the
|
|
debugger. This chapter illustrates these commands.
|
|
|
|
@iftex
|
|
In this sample session, we emphasize user input like this: @i{input},
|
|
to make it easier to pick out from the surrounding output.
|
|
@end iftex
|
|
|
|
@c FIXME: this example may not be appropriate for some configs, where
|
|
@c FIXME...primary interest is in remote use.
|
|
_0__
|
|
One of the preliminary versions of GNU @code{m4} (a generic macro
|
|
processor) exhibits the following bug: sometimes, when we change its
|
|
quote strings from the default, the commands used to capture one macro's
|
|
definition in another stop working. In the following short @code{m4}
|
|
session, we define a macro @code{foo} which expands to @code{0000}; we
|
|
then use the @code{m4} builtin @code{defn} to define @code{bar} as the
|
|
same thing. However, when we change the open quote string to
|
|
@code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
|
|
procedure fails to define a new synonym @code{baz}:
|
|
|
|
@smallexample
|
|
$ @i{cd gnu/m4}
|
|
$ @i{./m4}
|
|
@i{define(foo,0000)}
|
|
|
|
@i{foo}
|
|
0000
|
|
@i{define(bar,defn(`foo'))}
|
|
|
|
@i{bar}
|
|
0000
|
|
@i{changequote(<QUOTE>,<UNQUOTE>)}
|
|
|
|
@i{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
|
|
@i{baz}
|
|
@i{C-D}
|
|
m4: End of input: 0: fatal error: EOF in string
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Let's use _GDBN__ to try to see what's going on.
|
|
|
|
@smallexample
|
|
$ @i{_GDBP__ m4}
|
|
Reading symbol data from m4...done.
|
|
(_GDBP__)
|
|
@end smallexample
|
|
|
|
@noindent
|
|
_GDBN__ only reads enough symbol data to know where to find the rest
|
|
when needed; as a result, the first prompt comes up very quickly. We
|
|
then tell _GDBN__ to use a narrower display width than usual, so
|
|
that examples will fit in this manual.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{set width 70}
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Let's see how the @code{m4} builtin @code{changequote} works.
|
|
Having looked at the source, we know the relevant subroutine is
|
|
@code{m4_changequote}, so we set a breakpoint there with _GDBN__'s
|
|
@code{break} command.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{break m4_changequote}
|
|
Breakpoint 1 at 0x62f4: file builtin.c, line 879.
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Using the @code{run} command, we start @code{m4} running under _GDBN__
|
|
control; as long as control does not reach the @code{m4_changequote}
|
|
subroutine, the program runs as usual:
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{run}
|
|
Starting program: /work/Editorial/gdb/gnu/m4/m4
|
|
@i{define(foo,0000)}
|
|
|
|
@i{foo}
|
|
0000
|
|
@end smallexample
|
|
|
|
@noindent
|
|
To trigger the breakpoint, we call @code{changequote}. _GDBN__
|
|
suspends execution of @code{m4}, displaying information about the
|
|
context where it stops.
|
|
|
|
@smallexample
|
|
@i{changequote(<QUOTE>,<UNQUOTE>)}
|
|
|
|
Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879
|
|
879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]), argc, 1, 3))
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Now we use the command @code{n} (@code{next}) to advance execution to
|
|
the next line of the current function.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{n}
|
|
882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1]) : nil,
|
|
@end smallexample
|
|
|
|
@noindent
|
|
@code{set_quotes} looks like a promising subroutine. We can go into it
|
|
by using the command @code{s} (@code{step}) instead of @code{next}.
|
|
@code{step} goes to the next line to be executed in @emph{any}
|
|
subroutine, so it steps into @code{set_quotes}.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{s}
|
|
set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
|
|
at input.c:530
|
|
530 if (lquote != def_lquote)
|
|
@end smallexample
|
|
|
|
@noindent
|
|
The summary display showing the subroutine where @code{m4} is now
|
|
suspended (and its arguments) is called a stack frame display. We can
|
|
use the @code{backtrace} command (which can also be spelled @code{bt}),
|
|
to see where we are in the stack: it displays a stack frame for each
|
|
active subroutine.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{bt}
|
|
#0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
|
|
at input.c:530
|
|
#1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882
|
|
#2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
|
|
#3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
|
|
at macro.c:71
|
|
#4 0x79dc in expand_input () at macro.c:40
|
|
#5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Let's step through a few more lines to see what happens. The first two
|
|
times, we can use @samp{s}; the next two times we use @code{n} to avoid
|
|
falling into the @code{xstrdup} subroutine.
|
|
@smallexample
|
|
(_GDBP__) @i{s}
|
|
0x3b5c 532 if (rquote != def_rquote)
|
|
(_GDBP__) @i{s}
|
|
0x3b80 535 lquote = (lq == nil || *lq == '\0') ? def_lquote :\
|
|
xstrdup(lq);
|
|
(_GDBP__) @i{n}
|
|
536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\
|
|
(rq);
|
|
(_GDBP__) @i{n}
|
|
538 len_lquote = strlen(rquote);
|
|
@end smallexample
|
|
|
|
@noindent
|
|
The last line displayed looks a little odd; let's examine the variables
|
|
@code{lquote} and @code{rquote} to see if they are in fact the new left
|
|
and right quotes we specified. We can use the command @code{p}
|
|
(@code{print}) to see their values.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{p lquote}
|
|
$1 = 0x35d40 "<QUOTE>"
|
|
(_GDBP__) @i{p rquote}
|
|
$2 = 0x35d50 "<UNQUOTE>"
|
|
@end smallexample
|
|
|
|
@noindent
|
|
@code{lquote} and @code{rquote} are indeed the new left and right quotes.
|
|
Let's look at some context; we can display ten lines of source
|
|
surrounding the current line, with the @code{l} (@code{list}) command.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{l}
|
|
533 xfree(rquote);
|
|
534
|
|
535 lquote = (lq == nil || *lq == '\0') ? def_lquote : xstrdup\
|
|
(lq);
|
|
536 rquote = (rq == nil || *rq == '\0') ? def_rquote : xstrdup\
|
|
(rq);
|
|
537
|
|
538 len_lquote = strlen(rquote);
|
|
539 len_rquote = strlen(lquote);
|
|
540 @}
|
|
541
|
|
542 void
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Let's step past the two lines that set @code{len_lquote} and
|
|
@code{len_rquote}, and then examine the values of those variables.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{n}
|
|
539 len_rquote = strlen(lquote);
|
|
(_GDBP__) @i{n}
|
|
540 @}
|
|
(_GDBP__) @i{p len_lquote}
|
|
$3 = 9
|
|
(_GDBP__) @i{p len_rquote}
|
|
$4 = 7
|
|
@end smallexample
|
|
|
|
@noindent
|
|
That certainly looks wrong, assuming @code{len_lquote} and
|
|
@code{len_rquote} are meant to be the lengths of @code{lquote} and
|
|
@code{rquote} respectively. Let's try setting them to better values.
|
|
We can use the @code{p} command for this, since it'll print the value of
|
|
any expression---and that expression can include subroutine calls and
|
|
assignments.
|
|
|
|
@smallexample
|
|
(_GDBP__) p len_lquote=strlen(lquote)
|
|
$5 = 7
|
|
(_GDBP__) p len_rquote=strlen(rquote)
|
|
$6 = 9
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Let's see if that fixes the problem of using the new quotes with the
|
|
@code{m4} built-in @code{defn}. We can allow @code{m4} to continue
|
|
executing with the @code{c} (@code{continue}) command, and then try the
|
|
example that caused trouble initially:
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{c}
|
|
Continuing.
|
|
|
|
@i{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
|
|
|
|
baz
|
|
0000
|
|
@end smallexample
|
|
|
|
@noindent
|
|
Success! The new quotes now work just as well as the default ones. The
|
|
problem seems to have been just the two typos defining the wrong
|
|
lengths. We'll let @code{m4} exit by giving it an EOF as input.
|
|
|
|
@smallexample
|
|
@i{C-D}
|
|
Program exited normally.
|
|
@end smallexample
|
|
|
|
@noindent
|
|
The message @samp{Program exited normally.} is from _GDBN__; it
|
|
indicates @code{m4} has finished executing. We can end our _GDBN__
|
|
session with the _GDBN__ @code{quit} command.
|
|
|
|
@smallexample
|
|
(_GDBP__) @i{quit}
|
|
|
|
$
|
|
_1__@end smallexample
|
|
|